Technical advances in the design of components in the hotter-operating sections of gas turbine engines have produced increasingly complicated configurations to enhance the efficiency and performance. This is particularly the case with air-cooled parts such as hollow turbine blades. As a consequence, such parts have become very difficult and costly to manufacture.
One reported line of development describes fabrication of such complex parts from multiple members bonded at one or more junctures between them. Such bonding has been accomplished using intermediate or interlayer bonding materials, in the form of powders, coatings, shims, foils, etc., disposed between the members. The intermediate material is heated to a temperature which at least partially melts or liquefies such material to facilitate its diffusion between the opposing members being joined to produce a bonded joint. Associated with such reported methods are relatively high bonding temperatures required to bring about such melting so that relatively rapid interdiffusion and bonding can occur during part manufacture.
Further complicating such fabrication or bonding methods, are their attempted use in the joining of opposing members, each in the form of a single crystal. If the resultant bonded joint is multicrystalline or has a significant crystalline structural mismatch, for example, greater than approximately 5° with the opposing members, the joint can precipitate premature joint separation or failure, particularly in the transverse direction, within the relatively difficult environment and stress conditions experienced during gas turbine engine operation.